Short answers, pulled from the story.
The Daugava begins its journey in the Valdai Hills of Russia and ends by emptying into the Gulf of Riga of the Baltic Sea. This 1,020 kilometer waterway travels westward while tracing a large curve that bends south as it passes through northern Belarus.
Scholars have traced the name Dvina back to Indo-European roots rather than Uralic languages with Max Vasmer's Etymological Dictionary suggesting the word comes from Proto-Indo-European dānu meaning 'large river'. Finno-Ugric variants tell a different story about the nature of the flow where Livonian Estonian and Finnish names all stem from Proto-Finnic väin translating roughly to 'a large peacefully rolling river'.
Viking explorers crossed the Baltic Sea around the sixth century CE to enter the river and navigate upriver into the Baltic interior to connect with trade networks. Medieval times saw the Daugava become part of the route from Varangians to Greeks which transported furs from the north and Byzantine silver from the south.
The K egums Hydroelectric Power Station rose on the river from 1936 to 1939 while Pļaviņas Hydroelectric Power Station began operation in 1968 and the Riga Hydroelectric Power Plant followed in 1974. These structures altered the natural flow of the waterway significantly during Soviet-era construction projects that transformed the landscape.
Upstream of Jekabpils the pH value measures about 7.8 indicating slight alkalinity while nitrate levels reach approximately 0.82 milligrams per liter and ionic phosphate sits at 0.038 milligrams per liter. High nitrate and phosphate loads have contributed to extensive phytoplankton biomass buildup in the Baltic Sea and water pollution in Belarus is considered moderately severe with chief sources being treated wastewater and agricultural chemical runoff.